Sphacelaria cirrosa (Roth) C.Agardh

Scientific Description

Habit and structure. Thallus olive to dark brown, (0.2–)0.5–3 cm long, forming loose to dense tufts, epiphytic on various algae and seagrasses, arising from a basal cell plate or stoloniferous, occasionally with descending rhizoids from lower erect axes. Branching of the well developed, erect, axes abundant, with more or less determinate, evenly tapering laterals arising every few segments, subdistichously to more usually radially arranged, alternate to occasionally opposite, usually at wide angles to the axes and with the laterals narrower than the axes; phaeophycean hairs usually abundant, especially near tips of laterals, 10–15 µmin diameter. Axes 40–70(–80) µmin diameter with segments L/B (0.7–)1.0–1.3(–1.5)and showing 3–4(–8) longitudinal walls; laterals (20–)30–50 µmin diameter with segments L/B 0.8–1.2(–1.5) and showing 1–3 longitudinal walls; secondary transverse walls absent except in cells from which laterals arise.

Reproduction. Propagula with 3(–4) arms formed successively but soon becoming of equal length, each arm basally constricted and tapering above, 120–200(–350) µmlong and 15–35 µm in maximum diameter, borne on a pedicel (100)120–l60(–200) µm long, and with the apical cell usually developing into a hair but sometimes remaining as an umbonate cell. Unilocular sporangia often profuse, adaxial or scattered, single or opposite, shortly pedicellate, ovoid, (45–)50–65(–100) µmlong and 40–50 µmin diameter. Sexual plants with either plurilocular macrogametangia usually 55–85 µmlong and 40–65 µmin diameter, or microgametangia usually 65–100 µmlong and 35–60 µmin diameter; plurilocular sporangia may also occur. (Plurilocular organs not recorded for Australian plants.)

Distribution. In southern Australia, from Fremantle, W. Aust., to Port Jackson, N.S.W.

Habitat. S. cirrosa occurs in pools or calmer habitats; it varies considerably in robustness in different habitats.

[After Womersley, Mar. Benthic Fl. Southern Australia II: 164–166 (1987)]